Application of udder surface temperature by infrared thermography for diagnosis of subclinical mastitis in Holstein cows located in tropical highlands

摘要

Several reports have indicated that udder surfacetemperature (UST) can be a useful indicator of subclinicalmastitis (SCM). The objective was to evaluateUST by infrared thermography (IRT) as a diagnostictool for SCM and intramammary infection (IMI), andto assess the influence of environmental conditions inthe potential diagnosis of this disease in dairy cowslocated at high-altitude tropical regions. A total of 105cows (397 quarters) from 3 dairy farms with mechanicaland manual milking methods were enrolled in thestudy. Subclinical mastitis was diagnosed when quartersamples had a somatic cell count (SCC) ≥200 × 10~3cells/mL, microbial growth (MG) was defined whena major pathogen (≥1 cfu/plate) or Corynebacteriumspp. (≥10 cfu/plate) was isolated, and IMI was definedas the presence of MG and SCC ≥100 × 10~3 cells/mL. Infrared images were taken with a thermal cameraplaced 1 m away from the udder, and shots of the rearand left and right lateral view were made during themorning milking, before any manipulation of the udderand employing dark cardboard on the contralateralside to avoid artifacts in the background. A multilevelmixed effects linear regression model clustered withincows and herd was performed to evaluate the associationswith UST. Clinical performance was evaluatedusing the Youden index to establish the optimumUST thresholds, which were set at 32.6°C for any casedefinition when milking was by hand, at 33.7°C forMG, and at 34°C for SCM and IMI in machine-milkedquarters. Sensitivity (Se), specificity (Sp), area undercurve (AUC), and positive likelihood ratio (+LR) werealso assessed. Test agreement was assessed by kappacoefficient (κ). The UST of healthy quarters rangedbetween (95% CI) 32.4 and 32.6°C, lower than SCMquarters (n = 88) at 32.9°C (95% CI: 32.7–33.1 °C), MGquarters (n = 56) at 33.5°C (95% CI: 33.3–33.7°C), andIMI quarters (n = 50) at 33.5°C (95% CI: 33.2–33.7 °C).The UST was also related to the milking method:higher temperatures were observed for hand milking (n= 90) compared with machine milking (n = 185). Norelation between environmental conditions such as windspeed, atmospheric temperature, relative humidity, andtemperature-humidity index and UST were observedduring this study. For hand milking, the optimal USTthreshold was 32.6°C; for SCM, Se = 0.53, Sp = 0.89,AUC = 0.71, κ = 0.4; for MG, Se = 0.83, Sp = 0.93,AUC = 0.88, κ = 0.77; and for IMI, Se = 0.82, Sp= 0.92, AUC = 0.87, κ = 0.74. The machine milkingthreshold for SCM resulted in Se = 0.42, Sp = 0.97,AUC = 0.70, κ = 0.47; for MG, Se = 0.82, Sp = 0.89,AUC = 0.85, κ = 0.60; and for IMI, Se = 0.82, Sp =0.98, AUC = 0.90, κ = 0.79. These findings suggestthat UST determined by IRT is higher in machinemilkedcows and in quarters with MG and IMI than inhealthy quarters; therefore, UST by IRT is a reliable,clinically useful method for MG and IMI diagnosis.